The long term objectives of this proposal are: 1) to create a comprehensive quantified description of mastication in non-diseased human subjects and subjects with specific temporomandibular disorders (TMD) 2, to identify the specific features of mastication that differentiate between non-diseased human subjects and TMD subjects, 3) to identify time-dependent changes in the mastication of the TMD and non-diseased subjects over a three year period, and 4) to determine whether the level of masticatory dysfunction in TMD subjects is correlated with TMD symptom sign and severity. To fulfill these objectives, the proposed experiments will use a recently developed tool in order to create a detailed quantified description of jaw movement and EMG activity parameters in the subjects. The selected parameters have provided significant insight into mastication in previous studies. The measures of these parameters will then be used in a discriminant analysis to determine the extent to which the mastication of TMD subjects is different from the mastication of the non-diseased subjects. At the same time, the specific parameters that differentiate between the subject groups will be identified. Next, the masticatory parameters will be quantified repeatedly over a three year period and then analyzed with a multivariate analysis of variance, repeated measure design in order to identify time-dependent changes in mastication. Finally, a multivariate distance measure (i.e. the standard distance) between each TMD subject and the non-diseased group mean will be calculated. This distance measure defines how far each TMD subject is from the non- diseased group mean; therefore, it can be used as an "index of dysfunction". This index will be correlated with TMD symptom sign and severity in order to identify whether symptom severity and dysfunction severity are highly correlated. The proposed experiments are essential, since scientific work in the area of masticatory dysfunction has only just begun, and currently, much confusion exists regarding "normal" and "abnormal" mastication. The proposed studies will help significantly in reducing this confusion. They will provide valuable insight into the relationship between masticatory dysfunction and TMD disease progression. They will also provide significant information regarding masticatory adaptation processes. Finally, the study of associated EMG activity will provide invaluable information regarding electrophysiological changes associated with the disease. All of these results are critical in order to determine precisely the etiology, epidemiology, progression and treatment of TMD.